$\text{Ta có:}$ $\widehat{xOy}$ `=` $47^o$
$\text{Vì}$ $\widehat{xOy}$ $\text{và}$ $\widehat{xOy'}$ $\text{là hai góc đối đỉnh}$
$\Rightarrow$ $\widehat{xOy}$ `=` $\widehat{xOy'}$ `=` $47^o$
$\text{Vì đường thẳng xx' cắt đường thẳng yy' tại O}$
$\Rightarrow$ $\text{Ox và Ox' đối nhau}$
$\Rightarrow$ $\widehat{x'Oy}$ $\text{+}$ $\widehat{xOy}$ $\text{=}$ $180^o$
$\Rightarrow$ $\widehat{x'Oy}$ $\text{+}$ $47^o$ $\text{=}$ $180^o$
$\Rightarrow$ $\widehat{x'Oy}$ $\text{=}$ $180^o$ $\text{-}$ $47^o$
$\Rightarrow$ $\widehat{x'Oy}$ $\text{=}$ $133^o$
$\text{Vì}$ $\widehat{x'Oy}$ $\text{và}$ $\widehat{x'Oy'}$ $\text{là hai góc đối đỉnh}$
$\Rightarrow$ $\widehat{x'Oy}$ `=` $\widehat{x'Oy'}$ `=` $133^o$
